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Community and Q&A

Insulating a Balloon-Framed House

Marc_Cav | Posted in General Questions on

Hi All,

I’m somewhat new to the site.

I recently closed on a 1905 ballon framed house in central NY. According to I’m in climate zone 6.

Wall assembly from exterior in
Vinyl siding,1/2 foam, cedar clap board, thick tar paper, 3 1/2 stud, 3/4 board sheathing, 3/8 drywall.

The tar paper is fully intact but is compromised by the fasteners from the vinyl siding.

I’ll be removing the the drywall wall & 3/4 sheathing due to termite damage/mold. I plan to install 1/2 osb in place of the 3/4 sheathing to add strength to the house followed by 1/2 drywall.

I like the detail from one of Martin Holidays articles which is to add an air gap/air barrier/insulation but with existing hot water baseboard/ reducing the size of the stairwell so I can’t fur out the wall unless I remove the baseboard. Would adding spray foam be the best solution?

If yes could I spray it directly to the tar paper as long as there is no water intrusion? Also a spray foam contractor suggested using open cell, I thought closed would be best for this situation.

Alternatively I may add zip sheathing, and new siding down the road(if the price ever drops) so maybe adding 3” rockwool safe n sound flush to the interior of the stud allowing a 1/2” gap will be better than nothing until the time comes to re-side.

Open to any suggestions.



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  1. Expert Member
    PETER G ENGLE PE | | #1

    With that wall system, open cell might actually work OK. I used it in an 1890's Victorian with no ill effects. Your interior OSB will act as your semi-permeable vapor retarder with the rest of the wall drying easily to the exterior. Rockwool would be somewhat more climate-friendly and would also work for insulation, but you would have to be far more scrupulous in your air sealing details on the inside with that option.

  2. Marc_Cav | | #2

    Your reply makes me feel more confident with using open cell. Another bonus to open cell is it’s cheaper! Would it make a difference what side the osb faces to the exterior being that the smooth side has somewhat of a moisture resistant(So I’ve read)?

    On another note.
    I’m actually working on an 1890’s farm house (in much better shape than my house). Ended up going with closed cell. Of course this house has board sheathing on the exterior + it’s getting new siding so we’ll be able to add a wrb.

  3. Expert Member
    PETER G ENGLE PE | | #3

    Doesn't matter which way the OSB is oriented when it is your interior surface.

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